TUNABLE LASER MEASUREMENTS OF WATER VAPOR TRANSITIONS IN THE VICINITY OF 5 $\mu$m

Abstract

Selected line parameters of a number of infrared water vapor transitions in the 6.3 $\mu$m $\nu_{2}$ band have been measured using tunable semiconductor lasers with resolution better than $10^{-5}$$cm^{-1}$. The results further confirm earlier tunable laser work $^{1}$ which showed that high J rotational lines were substantially narrower than previously $estimated.^{2}$ The rotational quantum number J^{\prime\prime} of the lines observed range from 5 to 15. For all lines with $J^{\prime\prime} \geq 11$, the experimental widths have been found to be narrower than previous calculations, with the discrepancy becoming greater as J increases. For the measured lines where $J^{\prime\prime} \leq 8$, the experimental results still show some deviation from the calculated values. In addition, accurate values for pressure shifts, self-broadening, nitrogen and oxygen broadening coefficients are given for the first time. An experimental line shape study was also made on a number of lines and the shape was found to be Lorentzian over a range of up to three linewidths. A number of relative positions were also measured using a frequency scale generated by tuning the laser frequency through the transmission peaks of a Fabry-Perot interferometer. The data give further experimental checks on theoretical models for atmospheric transmission under a wide variety of atmospheric conditions.